A gas turbine engine may be used to power various types of vehicles and systems. A particular type of gas turbine engine that may be used to power aircraft is a turbofan gas turbine engine. A turbofan gas turbine engine may include, for example, five major sections, a fan section, a compressor section, a combustor section, a turbine section, and an exhaust section. The fan section is positioned at the front, or “inlet” section of the engine, and includes a fan that induces air from the surrounding environment into the engine, and accelerates a fraction of this air toward the compressor section. The remaining fraction of air induced into the fan section is accelerated into and through a bypass plenum, and out the exhaust section.
The compressor section raises the pressure of the air it receives from the fan section to a relatively high level. In a multi-spool engine, the compressor section may include two or more compressors. For example, in a triple spool engine, the compressor section may include a high pressure compressor, and an intermediate compressor. The compressed air from the compressor section then enters the combustor section, where a ring of fuel nozzles injects a steady stream of fuel. The injected fuel is ignited by a burner, which significantly increases the energy of the compressed air.
The high-energy compressed air from the combustor section then flows into and through the turbine section causing rotationally mounted turbine blades to rotate and generate energy. The air exiting the turbine section is exhausted from the engine via the exhaust section, and the energy remaining in this exhaust air aids the thrust generated by the air flowing through the bypass plenum.
Similar to the compressor section, in a multi-spool (e.g., multi-shaft) engine the turbine section may include a plurality of turbines. For example, in a triple spool engine, the turbine section may include a high pressure turbine, an intermediate pressure turbine, and a low pressure turbine. The energy generated in each of the turbines may be used to power other portions of the engine. For example, the low pressure turbine may be used to power the fan via one spool, the intermediate turbine may be used to power the intermediate pressure turbine via another spool that is concentric to the low pressure turbine spool, and the high pressure turbine may be used to power the high pressure compressor via yet another concentric spool.
The output power of a gas turbine engine may be controlled by controlling fuel flow rate to the engine, as well as controlling airflow through the engine. In particular, the fuel flow rate to the engine combustor section may be controlled, and the airflow into and through the compressor section may be controlled. In many aircraft applications, an engine controller such as, for example, a FADEC (Full Authority Digital Engine Controller), controls an engine fuel pressurization system, which may be configured to control both the fuel flow rate to the combustor section, and the airflow into and through the compressor section. In one particular fuel pressurization system, the engine fuel pressurization system may include, among other things, a fuel metering valve and a servo control valve, both of which are configured to respond to commands from the engine controller. The fuel metering valve and servo control valve are both connected to the fuel supply system. The fuel metering valve, in response to commands from the engine controller, controls fuel flow rate to the engine combustor section. The servo control valve, in response to commands from the engine controller, controls fuel flow through actuators coupled to a plurality of movable inlet guide vanes in the engine compressor section, which controls airflow into the engine compressor section.
Although the above-described system and method for controlling turbine engine inlet guide vanes is safe and generally reliable, it suffers certain drawbacks. For example, the fuel pump in the fuel pressurization system may need to be sized to not only deliver the appropriate amount of fuel to the combustor section, but to also supply the appropriate fuel flow rate and pressure to the inlet guide vane actuators. The fuel lines between the servo valves and inlet guide vane actuators are a potential fuel leakage source, which can lead to a postulated loss of engine thrust control. The inlet guide vanes in such systems are typically configured to move to the closed position under postulated abnormal conditions, and thus the engine may not be able to continue operating under such conditions.